Chart of ADSL and ADSL2+ Speed Versus Distance

While ISPs often advertise ADSL2+ and ADSL services as having maximum downlink connection speeds of 24 Mbps and 8 Mbps, respectively, very few broadband users can expect to achieve such speeds. As shown in the figure below, a broadband signal generally has to travel considerable distances along the copper cable from the exchange to the street cabinet (the so-called ‘E-side’), and then along another cable from the street cabinet to the nearby residential and business premises (the so-called ‘D-side’).

The broadband signal from the exchange suffers attenuation (loss) as it travels along the cable from the exchange to your broadband modem, reducing the speeds that can be delivered.

In general, the longer the total distance between your modem and the exchange, the more that signals are attenuated, as shown in the chart below.

Chart of ADSL2/2+ and ADSL connection speed against distance from the exchange

ADSL2+ provides most benefit for premises close to the exchange. For distances between 3 km and 3.5 km, where ADSL speeds have fallen well below 10Mbps, ADSL2+ and ADSL2 still provide worthwhile increases in connection speeds. There is very little difference in performance at distances above 4 km.

The table below provides the chart data in more granular form. Note that the length of the cables between your location and the BT exchange may be considerably more than the direct distance between your location and the exchange ‘as the crow flies’. This is because the cable first travels to a street cabinet, and there may be a number of possible routes.

Line loss (dB)

Line length (between premises and exchange) (km)

ADSL2/2+ speed (Mbps)

ADSL speed (Mbps)

1

0.07

24.0

8.0

2

0.15

24.0

8.0

3

0.22

24.0

8.0

4

0.29

24.0

8.0

5

0.36

24.0

8.0

6

0.43

24.0

8.0

7

0.51

24.0

8.0

8

0.58

23.9

8.0

9

0.65

23.8

8.0

10

0.72

23.7

8.0

11

0.80

23.5

8.0

12

0.87

23.3

8.0

13

0.94

23.0

8.0

14

1.01

22.7

8.0

15

1.09

22.4

8.0

16

1.16

22.1

8.0

17

1.23

21.7

8.0

18

1.30

21.4

8.0

19

1.38

21.0

8.0

20

1.45

20.6

8.0

21

1.52

20.2

8.0

22

1.59

19.7

8.0

23

1.67

19.3

8.0

24

1.74

18.8

8.0

25

1.81

18.2

8.0

26

1.88

17.6

8.0

27

1.96

16.8

8.0

28

2.03

16.2

8.0

29

2.10

15.7

8.0

30

2.17

15.0

8.0

31

2.25

14.4

8.0

32

2.32

13.9

7.9

33

2.39

13.4

7.9

34

2.46

12.9

7.9

35

2.53

12.3

7.8

36

2.61

11.8

7.8

37

2.68

11.2

7.7

38

2.75

10.5

7.5

39

2.82

10.0

7.3

40

2.90

9.5

7.1

41

2.97

9.0

6.9

42

3.04

8.5

6.7

43

3.11

8.0

6.5

44

3.19

7.5

6.2

45

3.26

7.1

5.8

46

3.33

6.7

5.6

47

3.40

6.3

5.4

48

3.48

6.0

5.2

49

3.55

5.6

5.0

50

3.62

5.3

4.8

51

3.69

5.0

4.6

52

3.77

4.7

4.4

53

3.84

4.4

4.2

54

3.91

4.2

4.0

55

3.98

3.9

3.8

56

4.06

3.7

3.6

57

4.13

3.4

3.4

58

4.20

3.2

3.2

59

4.27

2.9

2.9

60

4.35

2.7

2.7

61

4.42

2.5

2.5

62

4.49

2.3

2.3

63

4.56

2.1

2.1

64

4.63

2.0

2.0

65

4.71

1.8

1.8

66

4.78

1.7

1.6

67

4.85

1.6

1.4

68

4.92

1.5

1.2

69

5.00

1.4

1.0

70

5.07

1.3

0.8

Relationship between line loss, line length and downlink connection speeds for ADSL2+ and ADSL

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